1. Field of the Invention
The present invention relates to a free-wheel hub transmission mechanism for a bicycle.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional free-wheel hub transmission mechanism 10 according to U.S. Pat. No. 5,718,315 is shown to include an axle 12, a spoke mounting barrel 11 rotatably mounted on the axle 12 by means of first and second bearing units 14, a sprocket mounting barrel 13 which is rotatably mounted on the axle 12 by a third bearing unit 14 for driving the spoke mounting barrel 11 and which has a threaded portion 131 extending into the through-hole 111 of the spoke mounting barrel 11 and a sprocket mounting portion 132 extending outwardly of the spoke mounting barrel 11, and a sprocket (not shown) mounted on the sprocket mounting portion 132. A hollow reinforcing body 113 is provided in the through-hole 111 around the axle 12 and is coupled to the spoke mounting barrel 11 for simultaneous rotation therewith. A clutch barrel 15 is disposed in the through-hole 111 of the spoke mounting barrel 11 around the axle 12, and has a coupling portion which engages threadedly the threaded portion 131 of the sprocket mounting barrel 13 and a driving portion 151 which extends into and which drives the reinforcing body 113. A compression spring 16 is mounted in the through-hole 111 around the axle 12 to bias the clutch barrel 15 against the reinforcing body 113. A cup 18 is mounted in the through-hole 111 of the spoke mounting barrel 11 around the axle 12 and is secured in place by a respective lock nut 19 to stop the clutch barrel 15 and the compression spring 16 from moving to the right. The clutch barrel 15 is movable along the axle 12 toward the reinforcing body 113 for frictional engagement therewith upon rotation of the sprocket mounting barrel 13 in a first direction, thereby driving the reinforcing body 113 and the spoke mounting barrel 11 to co-rotate with the sprocket mounting barrel 13. The clutch barrel 15 is disengageable from the reinforcing body 113 upon rotation of the sprocket mounting barrel 13 in a second direction opposite to the first direction.
The reinforcing body 113 has a tapering bore for receiving and engaging frictionally the driving portion 151 of the clutch barrel 15.
The drawbacks of the aforementioned conventional free-wheel hub transmission mechanism are as follows:
A frictional clamping force (F) will result between the clutch barrel 15 and the reinforcing body 113 when the sprocket mounting barrel 13 rotates in the first direction. The clamping force (F) can be broken into axial and radial components (Fx,Fy), and the radial component (Fy) is usually absorbed during rotation of the assembly. However, the axial component (Fx) will cause an axial outward expelling effect on the reinforcing body 113 and the sprocket mounting barrel 13 relative to the spoke mounting barrel 11 that can affect smooth rotation of the hub transmission mechanism and that will result in a shorter service life.